For a variety of electronics, exposure to water is of concern due to water damage that can occur. For this reason, many companies are transitioning to product designs that prevent water intrusion. In doing so, such products should also maintain clear acoustics for the microphones and speakers that are present in the device. Manufacturers would like to rate their products with a minimum of IPx7. This rating specifies that their products could survive being submerged to a depth of 1 meter for ½ hour without damage. The 1-meter depth is measured at the bottom of the device, and the water depth is at least 15 cm at the top of the device, according to this rating. A filter or vent is necessary for electronic devices to allow for pressure equalization, allowing the transducers to function properly.
Acoustic vents are used to protect speakers and microphones from water and dust. Often these vents contain of expanded polytetrafluoroethylene (PTFE) membranes. Typically, such vents take the form of a disc being secured with an adhesive tape to the electronic housing that covers a transducer. The PTFE membrane prevents water and/or dust from reaching the microphone or speaker, while also allowing the acoustic signal to pass through with minimal loss.
PTFE membranes are used because they can be manufactured to have low basis weight and high flexibility. These properties allow them to vibrate easily when excited by an acoustic signal, and transmit the acoustic signal to the other side without allowing liquid intrusion. In addition, PTFE membranes are gas permeable, allowing equalizations of differential pressures due to temperature changes, as well as the evacuation of moisture due to condensation. PTFE membrane also has high dust efficiency and can withstand high differential water pressure without any liquid water passing through.
In electronic environments, PTFE membranes can be exposed to mechanical abrasion, high differential pressures, and mechanical prodding. These conditions can damage the PTFE by creating holes or stretching the membrane until it touches surrounding surfaces, thus compromising its ability to vibrate and transmit sound. The PTFE membrane can also be difficult to handle during conversion to finished parts. For this reason, a support layer is often laminated to the PTFE membrane in general non-acoustic venting applications. The support layer is most commonly a polymeric fabric.
It is generally understood that lamination of a support layer to a PTFE membrane dampens the ability of the membrane to transmit an acoustic signal. Some have recognized that this dampening effect can be too great to be acceptable in modern acoustic applications, particularly portable electronic applications in which the size of the vent is relatively small.
The lamination of a support layer can also prevent the vent from achieving the necessary waterproof rating. Typically acoustic vents are coupled to an adhesive tape which is then coupled to the electronics housing. Often the adhesive tape is affixed to the top surface of the support layer and does not make sealing contact with the PTFE, which is at least partially due to the thickness of the support layer. As such, water can enter the space between the PTFE and the adhesive/support layer.